The field of the disclosure relates generally to determination of signal propagation delay, and more specifically, to methods and systems for evaluation of signal propagation across disparate time domains.
As one relevant example, modern aircraft are configured with a multitude of systems. Many of these systems communicate to one another via communications buses. Certain of these systems receive information and/or data from a first bus, and one of the functions of such a system is to pass the information through to a second bus that is “time independent” from the first bus. Generally, the first system and the second system operate using independent clocking and therefore there is an inherent uncertainty regarding timing of events as indications of the events occurrence is passed from the first bus to the second bus. That is, the timing of the events that resulted in the information and/or data being transmitted onto the first bus generally is not identifiable when the information and/or data is processed by the system and output onto the second bus.
Such systems include, navigation, fuel monitoring, altitude sensors, communications, radar, autopilot, and in the case of military aircraft, various weapons and defense systems to name a very few. Such systems are generally made up of one or more components that operate together as a system and are typically programmed to provide the flight crew with one or more displays that provide status, and allow for flight crew input. As is easily understood, pilots are dependent on the data received on such displays for operation of the aircraft and for other aspects of a mission being performed via the aircraft, such as delivery of a payload and gathering of data.
The various components of such systems are often referred to as “line-replaceable-units” (LRUs). One type of LRU is a highly complex module often incorporating several processors for controlling and/or monitoring one or more components or subassemblies of an aircraft. Other LRUs are simple, such a mechanical device that outputs a signal based on a position of an engine nozzle. Certain LRUs may be provided to monitor and/or control one or more external devices such as an actuator, valve, motor, etc., associated with a particular component or assembly of the aircraft.
The various displays of an aircraft are also considered to be LRUs. Certain systems, for example, a navigation system may include several LRUs one of which is a dedicated display. A multi-function display may display navigation related data, as well as data from other systems, the data being displayed selectable by the pilot. Depending on a configuration of an avionics suite, one or both of the dedicated display and the multi-function display may communicate via one of the afore-mentioned communications buses.
An LRU typically also generates output signals which can be monitored to determine if the LRU and/or the component with which it is associated is not operating properly. In modern aircraft, such LRUs communicate on communications buses, and certain of these LRUs communicate on multiple buses, each bus having a disparate time domain. This situation leads to an inability to precisely determine the timing of events with respect to the second bus since the event timing is first bus dependent. It is easily understood that with the large amounts of data and information that are distributed among the various LRUs, situations may occur when a common timing reference for the multiple buses is desired.